(CNN) -- U.S. Sen. Tom Coburn announced Thursday that he will retire at the end of the current congressional session, ending his six-year term two years early.
The Oklahoma Republican, 65, has been battling cancer.
"But this decision isn't about my health, my prognosis or even my hopes and desires," he said in a statement.
"As a citizen, I am now convinced that I can best serve my own children and grandchildren by shifting my focus elsewhere. In the meantime, I look forward to finishing this year strong."
Coburn is a doctor who specialized in obstetrics before embarking on his political career.
"As dysfunctional as Washington is these days, change is still possible when 'We the People' get engaged, run for office themselves or make their voices heard. After all, how else could a country doctor from Muskogee with no political experience make it to Washington?" he wrote.
Before his time in the Senate, Coburn served in the U.S. House of Representatives from 1995 through 2001, according to a biography on his website.
In 2004, he was elected to serve in the Senate; he was re-elected in 2010.
Coburn and his wife have three children and seven grandchildren, according to the biography.
"My commitment to the people of Oklahoma has always been that I would serve no more than two terms. Our founders saw public service and politics as a calling rather than a career. That's how I saw it when I first ran for office in 1994, and that's how I still see it today," he wrote in Thursday's statement.
CNN's Dana Bash contributed to this report.